I don’t have experience with that but it sounds like a genuinely bad idea.
S3 isn’t optimized for performance or latency, so mounting an S3 bucket and using it for Graylog’s journal or any other latency-sensitive data will bring the performance of the whole thing to a grinding halt.
If you want to extend the storage space of an EC2 virtual machine, think about using an EBS volume (ideally with provisioned IOPS).
I found some other references on the internet that suggested it was a bad idea.
Is there any reference materials for disk sizing of the EBS volume. I know that my endpoints are producing around 250k a day in logs when saved as a text file.